1. Field of the Invention
This invention relates to the field of electrical engineering, and particularly to a method of balancing a rotor of an electrical machine and may be utilized for balancing a rotor with a liquid cooling system of the rotor winding of a high-power turbine generator.
2. Description of the Prior Art
The liquid cooling system of the rotor winding of such electrical machines is characterized by symmetrical distribution, on the rotor body, of several dozens of parallel hydraulic branches of the hydraulic duct of the liquid cooling system which is necessary for providing the heat balance of the rotor.
However, it is very difficult to agree all the parallel hydraulic branches in a strictly symmetrical relation. In addition, the hydraulic resistance of each of said branches is different because of the difference in internal dimensions of said branches, coupling sleeves, water delivery pipes etc., and also because of the difference in the degree of liquid flow turbulence therein.
The above facts lead to asymmetry in the distribution of the heat field across the active section of the rotor, to a temperature bend of the rotor and the heat unbalance thereof which in turn result in an increase in the allowable level of the rotor bearing vibration.
Moreover, the heat unbalance may be caused also by a redistribution of the liquid flow rate in the hydraulic branches of the hydraulic duct of the cooling system during the rotor operation when changes in operating conditions of an electrical machine take place. The level of rotor vibration must be constantly controlled and the vibrating condition of the rotor is to be adjusted to the accepted standard by balancing the rotor by means of various methods.
Prior art methods of balancing electrical machine rotors by elimination of the heat unbalance are labor-consuming, technologically inefficient, and do not provide for reliable rotor operation under all operating conditions.
Known in the art is a method of compensating the heat unbalance by mounting balancing loads (M. M. Isakovich, Z. I. Kleiman, B. H-Perchanock "Ustranenie vibratsii elektricheskih mashin". Energia Publishers, Moscow), 1969, p. 182). This method allows elimination of rotor unbalance and decreasing its vibration level to the predetermined standard only under certain operating conditions, for example under a rated load.
An inadmissible increase in rotor bearing vibration is observed when the operating conditions change to a reduced load or idling, and also when cooling system variables are changed.
Also known in the art is a method of compensating the heat unbalance by changing hydraulic resistances in the branches of the hydraulic duct of the rotor winding cooling system (M. M. Isakovich, Z. I. Kleiman, B. H-Perchanock "Ustranenie vibratsii elektricheskih mashin", Energia Publishers, Moscow, 1969, p. 182-183).
This method consists in preliminarily controlling the magnitude of bearing vibration and defining regions of the hydraulic duct of the cooling system, which cause a temperature bend of the rotor, and then providing such a temperature asymmetry across the cross section of the rotor which eliminates the temperature bend and the resulting increased vibration. This is attained by changing the hydraulic resistance in the branches of the hydraulic duct of the winding cooling system which are opposite to those branches which caused the temperature bend, for example by partially closing ventilation passages.
The precision of choice of said regions and the magnitude of the temperature asymmetry is monitored by variables of the bearing vibration under stable conditions of idling and load of the machine.
This method allows determining the branches of hydraulic duct of the cooling system for changing their hydraulic resistance only by way of tests requiring many times repeated labor-consuming operations of assembly and disassembly of the electrical machine.
After elimination of the temperature bend and obtaining an admissible level of vibration, with this method, the temperature field across the cross section of the rotor still remains nonuniform, and the machine so balanced can not reliably operate under all admissible conditions, since with a change of operating conditions the temperature field of the rotor changes and a temperature unbalance appears.
A principle object of the invention is to provide a more simple and reliable method of balancing a rotor of an electrical machine with a liquid cooling system of the rotor winding, which permits highly accurate detection and elimination of a heat unbalance of the rotor at rest.
Another object of the invention is to provide a method of balancing a rotor which provides the stability of admissible vibration characteristics under various operating conditions of an electrical machines.
Still another object of the invention is to provide a method whcih permits comparative analysis of variables of the rotor cooling conditions during the operation of an electrical machine.